This chapter analyses the methodological conditions for applying the notion of field to a specific kind of policy: water policy. It represents one of the few extensions of field theory into public policy outside the work of Bourdieu on housing. In that work, he approaches the policy by separating different levels of decisions and applying his theory to each independently. However, this research on the west of the USA explores the possibility of applying field theory on public policy by integrating all the levels into a common frame of analysis. We present the obstacles encountered in this process and the usefulness of field as an operative notion, rather than a fixed and closed theory.